The present invention generally relates to wheels of landing gear assemblies, of aircraft with electric drive taxi systems (ETSs).
ETSs powered by auxiliary power units (APUs) may now provide motive power for an increasing number of aircraft when the aircraft are taxiing from landing to the gate, and from the gate to the runway for takeoff. The ETS may provide the motive power as an alternative to motive power traditionally provided by a combination of aircraft main engines and separate carts. As ETSs are utilized for motive power in an increased number of taxis, for increasing distances, and for increased hours, it may be desirous to design components and systems to withstand greater stresses for greater periods of time to provide needed reliability and longer periods of time between needed repairs and maintenance.
The ETS may include a drive interface at an aircraft wheel to allow the wheel to be powered by an electric motor, powered by the APU. Traditionally, a driven gear may be attached to the wheel and a driving gear powered by the electric motor may be moved in and out of a driving connection with the driven gear. The driven gear and driving gear may be formed of a high strength steel to withstand stresses, as torque is transferred between them. The wheel to which the driven gear is attached may be formed of an aluminum alloy or different metal or material than the driven and driving gears. The wheel and driven gear may be attached with bolts or other attachment devices or methods.
The wheel and attached driven gear may be subject, regularly, to large changes in temperature, for example between heated brakes after landing and minus sixty-five degrees Fahrenheit (−65° F.) during flight. The differences in the expansion and contraction characteristics of the materials of the wheel and driven gear may create stresses at the interface between the wheel and the driven gear. In addition, differences in the flexibility characteristics of the materials of the wheel and the driven gear when the ETS provides motive power to the aircraft may also cause stresses at the interface between the wheel and the driven gear. As ETS is used for a larger percentage of aircraft taxiing, these stresses on the wheel and driven gear may cause wear or damage, and lead to less than desirous maintenance intervals for the landing gear.
Aircraft may have a weight limit on total aircraft and cargo weights. When high strength steel is used to form the driven gear, this may add to the aircraft weight and thus lessen the weight of cargo the aircraft is able to carry.
As can be seen, there may be an ongoing need to minimize stresses on aircraft wheels and driven gears, and in particular the interface between the wheel and the driven gear, and maximize maintenance intervals.